The effect of transition metal fluorides on the dehydrogenation and hydrogenation of MgH2 has been investigated. Many of the fluorides show a considerable catalytic effect on both the dehydrogenation temperature and hydrogenation kinetics of MgH2. Among them, NbF5 and TiF3 Most significantly enhance the hydrogenation kinetics of MgH2. It is suggested that hydride phases formed by the reaction between MgH2 and these transition metal fluorides during milling and/or hydrogenation play a key role in improving the hydrogenation kinetics of MgH2 (c) 2007 Elsevier B.V. All rights reserved.